My dog and going on carpet

My puppy is trained to go outside and on wee wee pad due to where we live and time constraints. She is not left along during day. I trained my last dog like this and it worked out well.

During the night when I get up to go to bathroom, I take her to the pad. She is a puppy and has to go sometimes.She always went on pad and that's it.

Lately, she walks away from pad and goes on a hallway carpet. I don't get it, for over a month we had a routine.

Any advice?

Re: My dog and going on carpet

Have you considered crate training? It really helps with house breaking.